Multiple standard inversion frequency measuring system



June 16, 1953 A. K. ROBINSON ETAL MULTIPLE STANDARD INVERSION FREQUENCY MEASURING SYSTEM Filed April 25, 1951 quencies may take any one of four forms.

may be a signal composed principally of a 10 mc.

Patented June 16, 1953 MULTIPLE STANDARD .INVERSION FRE` QUENCY MEAsUnING SYSTEM Alfred Ktltohinson, N ewport Beach, and William J. Ho'lert, Santa Ana, Calif.

Application April 23, 19351, Serial No. 222,515 i n Claims. (Cl.250--39') (Granted under Title 35, U. S. Code (1952),

sec. 266) The invention described Vherein many be vman- Y ufactured .and used by or for 'the Government of rthe United States for governmental purposes Without the payment yto us .of any royalty thereon in .accordance with the provisions of the act of April 30, 1928 (ch. 4:60, 45 Stat. L. 467). This invention relates to means for .and methods of measuring frequencies. l

It is an object of thisinvention to provide means for 'and methods of accurately and easquency and higher frequency ranges.

This object is accomplished in accordance with this invention by reducing the unknown frequency by known intervals until the signal is reduced to a point where vit can be conveniently compared 4with ;a known multiple of a low `frequency signal. f The invention may be clearly understood by referring to the following description and accompanying drawings, wherein the single gprovided by an audio oscillator 'I2 With .its Output connected to the oscilloscope 'I by a lineA `I3 ily measuring frequencies in the very high frey ure is a block diagram of a preferredembodiment of the invention.

In a preferred embodiment `of the invention illustrated in the drawing, a-conventionalmeans for measuring, frequencies in vthe 50-150 mc. range is provided. This means may take the form of a source I of various comparison frequencies connected by a line 2 to a 50e-150 mc.

heterodyne receiver 3 with a beat frequency oscil- The receiver is further adapted to relator. c'eive unknown frequencies in the 50-150 mc. range through a line 4.

The source l of various comparison frequencies comprises conventional harmonic generators, multivibrators and amplifiers. The source receives anfinput of known accuracy so that the frequencyof its output is ofV known accuracy.

The output of the source of comparison fret frequency and harmonics thereof from 50 to 150 mc. It may be a signal of 1 mc. and harmonics thereof from 50 to 150 mc. Or it may be 100 kc.

` and harmonics thereof, or 10 kc. and harmonics and `to the speaker I5 by line I3, :switch 9, vline I I, and line 6. I

The .audio :oscillator I2 may be connected by a switch I4 to .a 0 to -5000 c. p. is. multivibrator I5 which has alternative outputs-:of 1V` kc. and harmonics thereof., and c. p; s. Aand fharmonies thereof. The ymultivibrator I5 is` 'controlled by a signal from the source of'varicus comparsion frequencies I, and provides Iaccurate frequency reference .points to facilitate checking of the calibration onthe audiooscillat'o-r l2..

A. convenient alternative 'embodiment of the invention may have "a panoramic" 'adapter I6 connected by a lineyI'I to the intermediate frequency of the receiver 3.

Several alternative feeding an unknown signal in its original `or modified forms to the receiver 3. unknown may be received vby an antenna I8 fand fed by a line I9 through a switch 2I and the une 4 to the Vreceiver s. lAlternatively the origiv nal unknown may be fed from the linev I9 through a switchy 22 to a firstfrequency converter 23. The output of -the frequency converter 23 is "a modified unknown which is fedv 'through the switch 2| and line 4.,'to the receiver 3.k

Still another path for the unknown is provided from the antenna I8 directly to a second frequencyconverter 24. Y The output of the secondv frequency converter 24 is connected to the switch 22 and by a line 25 to the switch 2l. By operation of the switches 2I and 22, the loutput of the second frequency converter 24 `maybe `fed either throughfthe first frequencyfconverter4 23 to the receiver or. directly to the receiver 3.

The switch 2I .is provided with onemovable contact 2Ia-which is connected to the line 4, and with four stationaryncontacts 2lb, 2Ic,-2|d and 2Ie.. The.` stationary Vcontact '2lb -is connected `to the l-ine1I9. The stationary contact 2Ic is connected tothe output lofthe first frequency converter` 23 and the stationary contact 2 Id is connected by vthe line, 25 to the output of the second frequency converter 24. The fourth stationary contact 2 le indicates the open position o f the switch 2|.

simnany, the switch v2z is providecwtn a Y movable contact 22a which is connected toone input -of' theA first frequency converter 23-and with three stationary contacts 22h, 22o andv 22d. The stationary contact 22b'iis connected through the une vIsl to the antenna la and the stationary contact '22o is connecteddirectly to the output of.

paths are provided forv The original 'the second frequency converter 24.

Y pearingon the antenna The third stationary contact 22d indicates the open position of the switch 22.

Fixed comparison signals of various frequencies are fed tothe rst and second frequency converters 23 and 24 through a switch 26 and a line 21, and a switch 28 and a line 29, respectively. The switch 26 is provided with a movy able contact 26a which is connected to the line 21 and with three stationary contacts 26h, 26e, and 26d. The switch 28 is provided with a movable contact 28a and with five stationary contacts 28h, 28e, 28d, 28e and 281.

The source of the xed comparisonA frequencies which are fed to the frequency converters 23 and 24 may conveniently take the form of a primary standard 3I with a 100 kc. output and four harmonic generators 32, 33, 34 and 35 controlled by the primary standard 3I and with outputs of 300 mc., 400 mc., 900 mc. and harmonics thereof, and 800 mc. and harmonics thereof, 4respectively.

4 output of the source of Various comparison frequencies I, and the resulting difference frequency is determined by the receiver 3.

Frequency determination to the nearest 10 mc. can be made by the receiver-3 with the instrument 3l and instrumentI-set' to put out 10 mc. and harmonics thereof. Thel receiver is tuned with the beat frequency oscillator on to the unknown and then to each of the two adjacent comparision frequency harmonics. The receiver dial is sufficiently accurate to determine the frequency of the two harmonics which are known Y to be multiples of l0 mc, The change in the dial setting of the receiver when tuning from the unknown to the lower adjacent comparison f harmonic, as compared to the change in the dial setting of the receiver when tuning from theunknown to the higher adjacent comparison harmonic, will provide a good estimate of the lun- The first frequency converter 23 may receive a A fixed comparison frequency of 300 mc. by means of the line 21, the movable'switch contact 26a, .and the stationary switch contact 26o whichl is connected to the output Vof the 300 mc. harmonic generator 32;Y The rst frequency converter 23 may also receive a fixed comparison frequency of 400 mc. by means of the line 21, movable contact 26a, and stationary contact 26c which is connected to the output of the 400 mc. harmonic generator 33. The stationary contact 26d indicates the open position of the switch 25.

The second frequency converter 24 may receive a' fixed comparison frequency of 300 mc. by means of the line 29, the movable contact 28a and the stationary contact 28h which is connected to the output of theV 300 mc. harmonic generator 32 by a line 3B. The second frequency converter 24 may also receive 'a fixed comparison frequency of 900 mc. and harmonics thereof by means of the line 29, movable contact 28a'and the stationary contact 28o which is'connected to the output of the harmonic generator 34. The stationary contact 28d which is connected to the output of the harmonic generator 35 and the stationary contact 28e which is connected by a line 31 tothe output of the 400 mc. harmonic generator 33 provide means for feeding fixed comparison frequencies of 800 mc. and harmonics thereof, and 400' mc. to the second frequency converter 24 through the movable contact 28a andthe line 2B. The stationary switch terminal 23j indicates the open position of the'switch 28. Y

The frequencies ofthe four harmonicV generators 32, 33, 34 and 35V being multiples ofthe primary standard 3I, are of? the same percentage accuracy as the primary standard 3'I. The source ofthe variousl comparison frequencies I for the 50-{150 mc. frequency measurement range is also controlled'by the primary standard 3l. 1 It will be immediately Vapparent to all persons skilled in the art thatl amplifiers and tuners not specifically mentioned in this description may bedesirable additions to the circuit. rSince an understanding of the invention does not require. specific description of such instruments, they have been omitted in the interest of simplicity. Y

To measure frequencies in the range of 50-150 mc., the movable switch contacts 2Ia/and22av are' closed on terminals'ZIb and 22d. With this known.

Comparisonfrequencies of l mc. and harmonics thereof are then applied to the receiver 3.V ABy tuning from the l0 mc. point already'jdetermined to the unknown, and counting the 1 mc. points which are passed during that tuning, the unknown-can be determined to the nearest 1 mc.`

In like fashion, with the instrument set Vtoput out kc. and harmonics thereof, and then l0 kc. and harmonics thereof, determination to the nearest l0 kc. can be made. It will then be possible to'turn off the beat force oscillator and obtain an audio signal of 5000 cycles or less which can be observed aurally from the speaker 5 or visually on the oscilloscope 1.

' The audio output of the receiver 3 is beat against the variable output `of the audio oscillator I2 until a Vzero beat is obtained, and the frequency of the signal read'on the audio oscillator dial. Alternatively, the audio output of the receiver 3 is applied to one set of plates on the oscilloscope 1 and the variableVV output of the audio oscillator I2 is applied to the other. The audio oscillator is varied -until the pattern on the oscilloscope screen becomes round, and the frequency ofthe audio signal is read from theY audio oscillator dial. The frequency of this audio signal, when algebraically added to the known frequency of the comparison harmonic adjacent the unknown indicates the frequency of the unknown signal applied to the receiver 3 through line 4. 1

' To measure an unknownin a 15G-250 mc. band, the switches in the circuit are set as follows:-

movable contact 2I is closed on stationary con-f A tact 2Ic; movable contact 22a is closed on' sta- Y tionary contact 22h; movable contact 26a lis closed on stationary contact 23h; and movable contact 28a is closed on stationary contact 28j. The unknown is fed from the antenna I8 through the line I9 and the switch 22 tothe frequency converter 23. f Y y A 300 mc. signal is fed to the same frequency converter through switch 2S and line 21;- The output of the frequency converter 23 is the difference between the 300 mc. signal and the unknown-a difference which necessarily falls within the 50-150 mc. range which can be measured bythe receiver 3 as'previously described. rIhe original unknown at the antenna I8 is the algebraic sum of 300 mc. and the frequency determined-by the receiver 3.

Frequencies in the range .of Z50-350 mc. are measured in a similar manner using the 400 mc. harmonic generator 33 by setting movable contact 26a; at 6cA instead of 52612. Unknownsin I difference is not in theV 50-150 mc. range, accu,- with exactly the same switch settings that were rate measurement by the receiver 3 isnot affected. used for they 15S-250 mc. range, since the differ- The following table will indicate switch setence between the unknown andthe'SUO nic. sig- 5 tings and heterodyning frequencies for measurenal will still be in the 50-150 vmc.l range of ments up to 4150 mc.

the range 35(1450 mc. band `can be measured Second .First Signal Converter out Switch Positions put to Converter Output to Fg'glelcy Hetero- First Hetero- Receiver,

M c dyniug Converter dynlng Mc.

Freq., Mc. f Freq., Mc. 21 22 26 28 LMO-1,550.-. 1,550-1,650 1,650-1,750.

the receiver 3. Similarly, frequencies in the 450-550 mc. band may be measured with switch settings like those used in measuring the Z50-350 mc. band.

To measure frequencies in the 1550-650 mc. band, both the 300 mc. and the 400 mc. harmonic generators are used. The switches are set at Zic, 22e, 25h and 25e. The unknown is fed directly to the frequency converter 24 where it is mixed with the 400 mc. signal from the harmonic generator put oi' the frequency converter 2d will be 400 mc. lower than the unknown signal at the antenna i8. That output is then fed to thefrequency converter 23 through switch 22 where it is mixed with the signal from the 300 me. harmonic generator. An additional 300 mc. is subtracted from the unknown. The resultant output of the frequency converter Z3 will be within the 50450 mc. range of the receiver 3.

The range of measurements can be extended to the 1350-1450 band by heterodyning the i300y and 900 mc. signals in the frequency converter 24 and the 300 and 400 mc. signals in the frequency converter 23.

To measure frequencies in the range 1450 mc.1550 mc. the 800 mc. harmonic generator il@ is used alone, and the second harmonic or 1600 mc. output is used as the comparison frequency in the frequency converter 2li. The difference signal falls within the 50-150 mc. range which can be measured by the receiver 3. There is, of course also a difference signal resulting from beat with the soo me. signal, but since that 15 One component of the out- It should be noted, however, that the use of this system is not limited to 4150 mc. Any frequency up to infinity may be measured by the system simply by using higher harmonics of the 800 and 900 mc. signals.

The inexperienced operator may find it convenient to use a broad tuning receiver (not shown)v with a frequency range of 50-4000 mc. or higher to assist in identifying approximately the requency of the unknown signal s0 that he may know what Icombination of switch settings is requiredand what side band of what harmonic he is using. Experienced operators will be able to make such determinations by manipulation of tuning circuits in the frequency converters, by substitution for momentary observation of a primary standard which is slightly above or below 100 kc., or by other similar operations familiar to those in the art.

When study is being made of a weak or intermittent signal, it is often desirable to use a substitution oscillator (not shown) `in the 50-150 mc. range in lieu of the unknown signal fed to the receiver 3 through line 5.

Use of this invention reduces the unknown to an easily handled frequency Ibefore actual measurements are made, thus avoiding the difcult and sometimes impossible problem of obtaining a zero beat between two ultra high frequency or higher signals. This invention also' avoids the problem of determining which 10 kc. harmonic in the U. I-I. F. or higher range is the one at which zero beat has been obtained. Since primary standards are available many thousands of times fsa-,642,584

more accurate thanl Variable oscillators, this invention permits frequency determinations of an accuracy not possible with variable oscillator systems.

It will be understood that the embodiment shown and described is purely illustrative and that modifications may be made therein without departing from the spirit and scope of the inven- Ytion as set forth in the appended claims.

converted frequency and one of the frequenciesv from said source to a tunable receiver having means for indicating beats.

2. The method of claim 1 in which Vthe converted frequency is successively compared with selected frequencies of diiferent orders from said source to determine the frequency of said converted frequency.

3. In a frequency measuring device, a source of primary standard frequency, a harmonic vgenerator controlled by said primary standard frequency for providing a selected multiple of said primary standard frequency, converting means connected to said harmonic generator and to a source of unknown frequency for converting said unknown frequency into a converted frequency 8 differing from said unknown frequency by the amount of said selected multiple frequency, a harmonic source controlled by said primary standard frequency forV providing a selected harmonic, ltunable receiver means for indicating beats between two applied frequencies, means for applying said .converted frequency and said selected harmonic to said receiver means.

' 4. The combination of claim 3 in which a plurality of harmonic generators are provided each beingA controlled by said primary standard frequency and each of which generates a different .multiple of said primary standard frequency and in which switch means are provided for connecting a selected harmonic generator to said converter means.

5. The combination of claim 3 in which a second converting means and a plurality of harmonic generators are provided, the harmonic generators each being controlled by said primary standard frequency, in which switch means are provided to permit a selected harmonic generator to be connected to a selected converting means, and in which a selectively operable switch means is provided to connect the rst mentioned converter to the receiver means through the second converting means.

ALFRED K. ROBINSON. WILLIAM J. HOFFERT.

References Cited in the file of this patent UNITED STATES PATENTS Number 

